(navigation image)
Home American Libraries | Canadian Libraries | Universal Library | Community Texts | Project Gutenberg | Children's Library | Biodiversity Heritage Library | Additional Collections
Search: Advanced Search
Anonymous User (login or join us)
Upload
See other formats

Full text of "Text Book Of Mechanical Engineering"

782

Appendix II.

rately, a plaster cast is taken from each of the plaster blocks just
made. Now these carte, after drying, could not be fitted together,
for each is larger than its respective block by the thickness of the
casting ; but if each cast be separately impressed in sand, and the

two sand impressions fitted together, they will appear as at c, the
thickness space being left, into which the metal is run.

The casts having been varnished, will materially increase the
speed of moulding, for a pair of casts may. be divided between
two men, and the removal of the cast from the sand is more
expeditious than a thin pattern. The blocks may be retained for
future casts, but are of no use in moulding.

P. -27. Cubical Moulds in Loam.—Deeming it advisable
to illustrate flat mouldings in loam by at least one example, the
jet condenser, Fig. 763, has been chosen. The casting R consists
of a rectangular box containing a pump barrel, and having suitable
openings for exhaust, feed, and injection. It was formerly usual
to make complete patterns for such objects, but skeletons are now
largely adopted, the flat intermediate spaces being struck by loam
boards, In our case the wooden skeleton is seen in position in
the mould, being there shewn by the dense black portions, and
in describing its use we shall begin with the cope mould. An iron
plate A is placed on brick supports, and a coating of loam laid on,
which is then smoothed over with a plain board. The pattern
being set upon this bed, right side up, as at B, loam is filled in
round the side ; then, by using suitable striking-boards, as at 0
and c, the various flat surfaces are finished in facing loam, and a
pattern E embedded for the feed print. The skeleton is now
removed vertically, but the bottom strips FF, and the feed flange,